Analysis And Optimization Of Axial Electromagnetic Force In Axial-flux Permanent Magnet Vernier Machine

Axial-flux permanent magnet vernier machine(PMVM)has the advantages of high torque density and compact axial structure,therefore,it has drawn much attention in the field of direct-drive which features on low-speed and high torque.In order to improve the power factor and power density,the development of axial-flux PMVM tends to be multi-layered.The disk-shaped rotor of an axial-flux PMVM has a tendency to axial translation and deflection under the action of huge and unbalanced axial electromagnetic force,and even an accident may occur,making it difficult for the machine to operate steady.Recent research shows that axial electromagnetic force is one main source of operating noise for axial-flux PMVM.Therefore,this dissertation proposes four basic models of axial-flux PMVM with similar radial structure,aiming to analyze and optimize the axial electromagnetic force,and compare characteristics with different models.In this dissertation,the three-dimensional and two-dimensional finite element models of surface-mounted permanent magnet(SPM)and interior permanent magnet(IPM)axial-flux PMVM with single stator and single rotor are constructed.The axial electromagnetic force of these models are analyzed and compared.Subsequently,the expression of axial electromagnetic force are deduced by analytical methods,including axial electromagnetic force density and axial electromagnetic force of whole rotor.Afterwards,the radial electromagnetic force distribution of axial-flux PMVM with similar radial structure is studied through theory and simulation.The axial electromagnetic force of SPM and IPM axial-flux PMVM with single stator and single rotor are optimized in this dissertation.Firstly,through theoretical analysis,several motor structural parameters sensitive to axial electromagnetic force are selected as optimization variables.The effects of optimization variables on the objective functions such as the output torque,the axial electromagnetic force and the peak density of axial electromagnetic force density are analyzed.Secondly,based on the simulation database of the appropriate value interval of the optimization variables,a Kriging prediction model of the optimization variable and the objective function is constructed.Genetic algorithm is applied to search optimization result based on the prediction model.Finally the results are verified by finite element simulation.In order to verify the suppression of the axial electromagnetic force of the whole rotor by the multilayer structure,this dissertation constructs three-dimen-sional and two-dimensional finite element models of SPM and IPM axial-flux PMVM with dual-stator and single rotor,and analyzes the axial electromagnetic force density and axial electromagnetic force of the whole rotor of the two models through simulation and analytical method.Finally,conclusions are drawn through comparisons among four basic models of axial-flux PMVM.